Method for manufacturing metal container, apparatus for manufacturing metal container, and metal container

ABSTRACT

A method for manufacturing a metal container includes a first step of forming a substantially planar four-sided bag using a metal plate; a second step of sandwiching, by first and second parallel plate jigs, one surface and the other surface of the four-sided bag formed in the first step; and a third step of pressurizing an inside of the four-sided bag while maintaining a contact state by the first and second parallel plate jigs with respect to the four-sided bag sandwiched between the first and second parallel plate jigs in the second step, and expanding a volume space in the four-sided bag while increasing a distance between the first and second parallel plate jigs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application No.PCT/JP2021/032551, which was filed on Sep. 3, 2021 based on Japanesepatent application 2020-162436 filed on Sep. 28, 2020, whose contentsare incorporated herein by reference. Also, all the references citedherein are incorporated as a whole.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a method for manufacturing a metalcontainer, an apparatus for manufacturing the metal container, and themetal container.

Background Art

In related art, there has been a method of performing deep drawing bysandwiching and fixing a peripheral end portion of a metal platematerial such as stainless steel and pushing a central portion with apunch (for example, see PTL 1).

CITATION LIST Patent Literature

PTL 1: JP2010-247172A

SUMMARY

The inventors of the present application have studied a hollow containerincluding a vacuum insulated core material such as powder therein. Thehollow container can be manufactured by combining two plate materialsformed by the deep drawing described in PTL 1. However, in the methoddescribed in PTL 1, since elongation is locally generated in a metalplate during molding, the metal plate may be broken due to theelongation.

It is highly difficult to mold the metal plate in a manner of packagingthe core material with a packaging paper, and in order to maintain avacuum, sealing is performed at each location of the metal plate afterthe packaging, but it is difficult to perform sealing on athree-dimensional molded article, and there are too many locations to besealed, which is not practical.

Therefore, an envelope shaped four-sided bag is prepared, and it isattempted to prepare a container having a substantially truncated squarebipyramidal shape (shape in which bottom surface sides of two truncatedquadrangular pyramids including no bottom surface are connected to eachother) or a substantially rectangular parallelepiped shape by gaspressure molding. However, it has been found that even when the gaspressure molding is performed using the four-sided bag, the four-sidedbag is broken due to excessive elongation of a material during themolding.

According to an embodiment, a method for manufacturing a metal containerand an apparatus for manufacturing the metal container can preventbreakage due to local elongation of a metal plate when forming acontainer from a four-sided bag.

Solution to Problem

A method for manufacturing a metal container according to an embodimentincludes: a first step of forming a substantially planar four-sided bagusing a metal plate; a second step of sandwiching, by first and secondparallel plate jigs, one surface and the other surface of the four-sidedbag formed in the first step; and a third step of forming, using thefour-sided bag, a container having a substantially truncated squarebipyramidal shape or a substantially rectangular parallelepiped shape bypressurizing an inside of the four-sided bag while maintaining a contactstate by the first and second parallel plate jigs with respect to thefour-sided bag sandwiched between the first and second parallel platejigs in the second step, and expanding a volume space in the four-sidedbag while increasing a distance between the first and second parallelplate jigs.

An apparatus for manufacturing a metal container according to anembodiment including first and second parallel plate jigs configured tosandwich one surface and the other surface of a substantially planarfour-sided bag formed of a metal plate, in which

-   the first and second parallel plate jigs are capable of sandwiching    the four-sided bag, and maintain a contact state with the one    surface and the other surface of the four-sided bag in a process of    pressurizing an inside of the four-sided bag to expand a volume    space in the four-sided bag.

A metal container according to an embodiment is a metal container havinga substantially truncated square bipyramidal shape or a substantiallyrectangular parallelepiped shape. The metal container includes: twoquadrangular top plates formed as one surface of the container and theother surface opposite to the one surface; a plurality of side wallsconnecting the two top plates; and an ear portion having oblique sidesapproaching each other from opposing vertexes of the two top plates andprotruding laterally or folded along the plurality of side walls,valley-folded portions are formed at boundaries between the ear portionand the plurality of side walls, and one or more valley-folded markshaving the vertex as a rotation center are formed between thevalley-folded portion and the oblique side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective view showing metal containersmanufactured by methods for manufacturing the metal containers accordingto an embodiment of the present invention, in which FIG. 1A shows afirst metal container, and FIG. 1B shows a second metal container.

FIG. 2 is an enlarged view of a periphery of an ear portion shown inFIG. 1A.

FIG. 3 is a perspective view showing a four-sided bag used formanufacturing the metal container.

FIGS. 4A and 4B are a schematic configuration diagrams showing a mainpart of an apparatus for manufacturing the metal container according tothe present embodiment, in which FIG. 4A is a plan view, and FIG. 4B isa side view.

FIGS. 5A and 5B are partially enlarged views showing details of a secondflap jig shown in FIGS. 4A and 4B, in which FIG. 5A shows a maximumprotruding state of a wedge, and FIG. 5B shows a minimum protrudingstate of the wedge.

FIGS. 6A and 6B are perspective views showing an intermediate process ina process of forming a container having a substantially rectangularparallelepiped shape, in which FIG. 6A shows a first stage, and FIG. 6Bshows a second stage.

FIGS. 7A, 7B and 7C are perspective views showing a forming process ofthe four-sided bag, in which FIG. 7A shows a metal plate, FIG. 7B showsa state in which the metal plate is folded, and FIG. 7C shows thefour-sided bag.

FIGS. 8A, 8B, 8C and 8D are process diagrams showing the process offorming the container having the substantially rectangularparallelepiped shape from the four-sided bag, in which FIG. 8A shows astage in which the four-sided bag is sandwiched, FIG. 8B shows the firststage in which an inside is pressurized, FIG. 8C shows the second stagein which the inside is pressurized, and FIG. 8D shows a completion stageof the container.

FIGS. 9A and 9B are perspective views showing other examples of thefour-sided bag, in which FIG. 9A shows a first example, and FIG. 9Bshows a second example.

FIG. 10 is a plan view showing an auxiliary plate.

FIG. 11 is an enlarged view of a periphery of an ear portion accordingto a modification.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in accordance witha preferred embodiment. The present invention is not limited to thefollowing embodiment, and can be modified as appropriate withoutdeparting from the scope of the present invention. In the embodiment tobe described below, some configurations are not illustrated ordescribed, but it goes without saying that a known or well-knowntechnique is applied as appropriate to details of an omitted techniquewithin a range in which no contradiction occurs to contents to bedescribed below.

FIGS. 1A and 1B are perspective views showing metal containersmanufactured by methods for manufacturing the metal containers accordingto the embodiment of the present invention, in which FIG. 1A shows afirst metal container, and FIG. 1B shows a second metal container.

As shown in FIG. 1A, a metal container C manufactured in the presentembodiment is, for example, a container C1 having a substantiallyrectangular parallelepiped shape, and includes two quadrangular topplates TB formed as one surface of the container C1 and the othersurface opposite to the one surface, a plurality of side walls HPconnecting the two top plates TB, and a plurality of ear portions Dprotruding from four corners of the container C1 in a manufacturingprocess. A seam welding portion SW is formed at an end portion on a longside LS side. On the other hand, an end portion on a short side SS sideorthogonal to the long side LS (an intermediate portion of the shortside SS) is an edge side E which is not welded or the like.

As shown in FIG. 1B, the metal container C manufactured in the presentembodiment is, for example, a container C2 having a substantiallytruncated square bipyramidal shape. In the present embodiment, atruncated square bipyramid is one obtained by connecting bottom surfacesides of truncated quadrangular pyramids including no bottom surface.Similarly to the container C1, the container C2 includes twoquadrangular top plates TB formed as one surface of the container C2 andthe other surface opposite to the one surface, a plurality of side wallsHP connecting the two top plates TB, and a plurality of ear portions Dprotruding from four corners of the container C2 in a process ofmanufacturing the container C2. A seam welding portion SW is formed atan end portion on a long side LS side. Further, an end portion on ashort side SS side orthogonal to the long side LS is also an edge side Ewhich is not welded or the like.

In each of the containers C1 and C2, the seam welding portion SW may beformed on the short side SS side by the manufacturing method, or theseam welding portions SW may be formed on both the long side LS side andthe short side SS side (four sides).

FIG. 2 is an enlarged view of a periphery of the ear portion D shown inFIG. 1A. As shown in FIG. 2 , the ear portions D has oblique sides HYthat approach each other from opposing vertexes V of the two top platesTB and protrudes laterally. Here, opposing means opposing in a directionconnecting one surface and the other surface. A valley-folded portion VFwhich is valley-folded is formed between such an ear portion D and theside wall HP.

Further, a plurality of valley-folded marks VT having the vertexes V asrotation centers are formed between the valley-folded portion VF and theoblique sides HY. The number of the valley-folded marks VT may be one.As will be described later, the valley-folded marks VT are portions thatwere the valley-folded portions VF in the past in the manufacturingprocess of the container C1, and are portions in which traces that hadbeen valley-folded in the past remains.

Although FIG. 2 illustrates the periphery of one ear portion D in FIG.1A, the same applies to other ear portions D. Although a description isomitted, similarly, in the container C2 having the substantiallytruncated square bipyramidal shape shown in FIG. 1B, a plurality ofvalley-folded marks VT having vertexes V as rotation centers are formedbetween valley-folded portion VF and oblique sides HY. The number of thevalley-folded marks VT may be one.

Such a metal container C shown in FIGS. 1A and 1B is manufactured from afour-sided bag. FIG. 3 is a perspective view showing the four-sided bagused for manufacturing the metal container C. As shown in FIG. 3 , afour-sided bag B is a bag member having a substantially planarquadrangular shape (square shape or rectangular shape) formed by foldingor welding a metal plate (for example, a stainless steel plate having athickness of about 0.1 mm) MP (see FIGS. 7A and 7C to be describedlater). Four sides of the four-sided bag B are in a closed state exceptfor an opening to be described later. The opening (small hole) forinternal pressurization is formed in the four-sided bag B. An inside ofsuch a four-sided bag B is pressurized through the opening, and aninternal volume space thereof is expanded. After the expansion of thevolume space, the opening is sealed, and the metal container C as shownin FIGS. 1A and 1B is manufactured.

FIGS. 4A and 4B are schematic configuration diagrams showing a main partof an apparatus for manufacturing the metal container C according to thepresent embodiment, in which FIG. 4A is a plan view, and FIG. 4B is aside view. As shown in FIGS. 4A and 4B, a manufacturing apparatus 1includes first and second parallel plate jigs 11 and 12. As shown inFIG. 4A, the first and second parallel plate jigs 11 and 12 are flatplates having a quadrangular (substantially square shape or rectangularshape) in a plan view. Although only one surface side of themanufacturing apparatus 1 is illustrated in FIG. 4A, the second parallelplate jig 12 and flap jigs F to be described later on the other surfaceside also have the same shape as the first parallel plate jig 11 andflap jigs F on the one surface side. The first and second parallel platejigs 11 and 12 are smaller than an area of the four-sided bag B in theplan view, and sandwich one surface and the other surface of thefour-sided bag B in a state of being located inside four sides of thefour-sided bag B. The sides of the first and second parallel plate jigs11 and 12 are parallel to the four sides of the four-sided bag B so asto sandwich the one surface and the other surface of the four-sided bagB. The first and second parallel plate jigs 11 and 12 form the topplates TB of the metal container C.

The manufacturing apparatus 1 further includes a plurality of flap jigsF. The flap jigs F sandwich four regions around regions sandwiched bythe first and second parallel plate jigs 11 and 12 on the one surfaceand the other surface of the four-sided bag B, that is, end portionsides of the four-sided bag B. The flap jigs F are pivotable asindicated by arrows A1 in of FIGS. 4A and 4B, and forms side surfaces ofthe container C1 having the substantially rectangular parallelepipedshape or oblique surfaces of the container C2 having the substantiallytruncated square bipyramidal shape.

As shown in FIGS. 4A and 4B, the flap jigs F are initially in a state ofbeing substantially parallel to the first and second parallel plate jigs11 and 12, and pivote from the substantially parallel state to apredetermined angle with respect to the parallel state in themanufacturing process (see FIGS. 8A to 8D to be described later). Thepredetermined angle is 90° in the manufacturing apparatus 1 formanufacturing the container C1 having the substantially rectangularparallelepiped shape, and the predetermined angle is less than 90° inthe manufacturing apparatus 1 for manufacturing the container C2 havingthe substantially truncated square bipyramidal shape.

As shown in FIGS. 8A to 8D, the flap jigs F are configured to movetoward a center side of the four-sided bag B in the manufacturingprocess. Accordingly, in the manufacturing process of the metalcontainer C, the flap jigs F move to the center side of the four-sidedbag B while pivoting, and operate in a manner of folding the metalcontainer C from the sides.

Here, the first and second parallel plate jigs 11 and 12 are connectedto the flap jigs F via link mechanisms L. Therefore, the flap jigs Foperate in a manner of moving toward the center side of the four-sidedbag B while pivoting in accordance with the operation in which the firstand second parallel plate jigs 11 and 12 move in directions away fromeach other. The flap jigs F are formed in a manner of gradually foldingthe metal container C from the sides as a space volume inside thefour-sided bag B increases. Wedges W, which will be described later,also operates in conjunction with the operations of the first and secondparallel plate jigs 11 and 12 via the link mechanisms L.

The plurality of flap jigs F include a plurality of first flap jigs F1that sandwich two opposing regions (two regions on seam welding portionSW sides in the present embodiment) of the four regions, and a pluralityof second flap jigs F2 that sandwich remaining two opposing regions (tworegions on edge side E sides in the present embodiment) of the fourregions. As shown in FIG. 4A, the first flap jig F1 has a trapezoidalshape in the plan view. On the other hand, the second flap jig F2includes a main body portion H having a rectangular shape in the planview, and wedges W on both end portion sides of the main body portion H(that is, corner portion sides of the four-sided bag B).

FIGS. 5A and 5B are partially enlarged views showing details of thesecond flap jig F2 shown in FIGS. 4A and 4B, in which FIG. 5A shows amaximum protruding state of the wedge W, and FIG. 5B shows a minimumprotruding state of the wedge W.

Each of the wedges W includes a line segment portion W1 extending from arespective one of the vertexes V of the first and second parallel platejigs 11 and 12 toward a side of the four-sided bag B on a second flapjig F2 side (that is, the edge side E). In the apparatus 1 formanufacturing the metal container C, the wedges W move the line segmentportions W1 in a process of pressurizing the inside of the four-sidedbag B and increasing the internal space volume.

Specifically, as shown in FIG. 5B, the wedge W moves toward a main bodyportion H side while rotating such that an angle θ formed by the linesegment portion W1 and the side of the four-sided bag B on the secondflap jig F2 side (that is, the edge side E) changes from an acute angleto a right angle. At this time, an amount of movement of the wedge W iscontrolled by cooperation of a spring SP shown in FIGS. 5A and 5B, anoval portion LH formed in the main body portion H, and a screw portion Sintegrally connected to the wedge W and fitted into the oval portion LH.The rotation of the wedge W is controlled by an appropriate means (notshown). With such a wedge W, the apparatus 1 for manufacturing the metalcontainer C according to the present embodiment can be formed in amanner of further folding the container C, as shown in FIGS. 6A and 6Bto be described later.

FIGS. 6A and 6B are perspective views showing an intermediate process ina process of forming the container C1 having the substantiallyrectangular parallelepiped shape, in which FIG. 6A shows a first stage,and FIG. 6B shows a second stage. In the present embodiment, thecontainer C1 having the substantially rectangular parallelepiped shapeis formed through the first stage shown in FIG. 6A and the second stageshown in FIG. 6B.

Here, as shown in FIG. 6A, in the present embodiment, the container C1having the substantially rectangular parallelepiped shape is formed in amanner of performing folding while pressurizing the inside of thefour-sided bag B, and thus the valley-folded portions VF shown in FIG.6A are formed. Next, when the internal volume is further increasedthrough the internal pressurization of the four-sided bag B, thevalley-folded portions VF shown in FIG. 6B are formed.

When the valley-folded portions VF shown in FIGS. 6A and 6B arecompared, the angles θ with respect to the edge side E are different.That is, when the container C1 is formed by folding the four-sided bagB, the angles θ of the valley-folded portions VF with respect to theedge side E change. The apparatus 1 for manufacturing the metalcontainer C according to the present embodiment moves the line segmentportion W1 of the wedge W as shown in FIG. 5B in accordance with thechanging angle θ, whereby the container C1 can be formed in a manner offolding the container C1 more appropriately.

Although the container C1 having the substantially rectangularparallelepiped shape has been described above as an example, the sameapplies to a case where the container C2 having the substantiallytruncated square bipyramidal shape is formed.

Next, a method for manufacturing the metal container C according to thepresent embodiment will be described. FIGS. 7A, 7B and 7C areperspective views showing a forming process of the four-sided bag B, inwhich FIG. 7A shows the metal plate MP, FIG. 7B shows a state in whichthe metal plate M is folded, and FIG. 7C shows the four-sided bag B.

First, as shown in FIG. 7A, the rectangular metal plate MP is prepared.Next, as shown in FIG. 7B, short sides MP1 of the rectangular metalplate MP are bent so as to face each other. Here, bent portions are theedge sides E described above. Thereafter, as shown in FIG. 7C, the shortsides MP1 are butt-welded to each other to form a butt-welded portionBW. On the other hand, sides orthogonal to the edge sides E areseam-welded to form seam welding portions SW. As described above, themetal plate MP is formed into the substantially planar four-sided bag B.

FIGS. 8A, 8B, 8C and 8D are process diagrams showing the process offorming the container C1 having the substantially rectangularparallelepiped shape from the four-sided bag B, in which FIG. 8A shows astage in which the four-sided bag is sandwiched, FIG. 8B shows the firststage in which the inside is pressurized, FIG. 8C shows the second stagein which the inside is pressurized, and FIG. 8D shows a completion stageof the container C1.

First, as shown in FIG. 8A, the four-sided bag B is sandwiched betweenthe first and second parallel plate jigs 11 and 12. At this time, theone surface and the other surface of the four-sided bag B are sandwichedbetween the first and second parallel plate jigs 11 and 12 such that thefirst and second parallel plate jigs 11 and 12 are located inside thefour sides of the four-sided bag B and the four sides of the four-sidedbag B are parallel to the respective sides of the first and secondparallel plate jigs 11 and 12.

Further, as shown in FIG. 8A, the flap jigs F sandwich the four regionsaround the regions sandwiched by the first and second parallel platejigs 11 and 12, that is, the end portion sides of the four-sided bag B.More specifically, as shown in FIG. 4A, the two opposing regions of thefour regions are sandwiched by the first flap jigs F1, and the remainingtwo opposing regions of the four regions are sandwiched by the secondflap jigs F2.

As shown in FIG. 8A, in the present embodiment, an air bag AB isdisposed between an upper wall UW of the manufacturing apparatus 1 andthe like and the first parallel plate jig 11. Accordingly, the air bagAB presses the first parallel plate jig 11, and a reaction force (forcein a direction of preventing expansion) is applied when the volume spaceis expanded. Furthermore, the reaction force is similarly applied to thesecond parallel plate jig 12 that is interlocked with the first parallelplate jig 11, and the flap jigs F that are interlocked with the firstand second parallel plate jigs 11 and 12 via the link mechanisms L.

Next, the inside of the four-sided bag B is pressurized from a state inFIG. 8A. Accordingly, the volume space of the four-sided bag B isexpanded as shown in FIGS. 8B and 8C. When the reaction force of the airbag AB is applied in this expansion process, the four-sided bag Bmatches the shapes of the first and second parallel plate jigs 11 and 12and the flap jigs F. That is, the first and second parallel plate jigs11 and 12, and the flap jigs F increase the space volume of thefour-sided bag B while maintaining a contact state with the four-sidedbag B.

In the process of expanding the volume space of the four-sided bag B asshown in FIGS. 8B and 8C, the line segment portion W1 of the wedge Wapproaches the main body portion H while rotating as shown in FIG. 5B.Accordingly, as shown in FIGS. 6A and 6B, the valley-folded portions VFcorresponding to a size of the volume space are formed.

Thereafter, the volume space is further expanded, and the container C1having the substantially rectangular parallelepiped shape is formed asshown in FIG. 8D.

In the case of forming the container C2 having the substantiallytruncated square bipyramidal shape instead of the container C1 havingthe substantially rectangular parallelepiped shape, the process may befinished in a state in FIG. 8C, for example, without pressurizing theinside of the four-sided bag B to a state shown in FIG. 8D.

The flap jigs F are not limited to the case of sandwiching the fourregions, and may sandwich only two or three of the four regions. This isbecause a certain folding effect can also be achieved in this case.

In this manner, according to the method and the apparatus 1 formanufacturing the metal container C according to the present embodiment,since the inside of the four-sided bag B is pressurized whilemaintaining the contact state by the first and second parallel platejigs 11 and 12 with respect to the four-sided bag B and the volume spaceinside the four-sided bag B is expanded while increasing a distancebetween the first and second parallel plate jigs 11 and 12, in thefour-sided bag B having relatively high rigidity on an end portion sideand relatively low rigidity on a center side, the inside of thefour-sided bag B is pressurized while reducing a portion havingrelatively low rigidity, and when the container is formed from thefour-sided bag B, it is possible to prevent breakage due to localelongation of the metal plate MP.

At least two of the four regions are sandwiched by the plurality of flapjigs F that can move toward the center side of the four-sided bag whilepivoting, and the inside of the four-sided bag B is pressurized whilemaintaining the contact state by the first and second parallel platejigs 11 and 12 and maintaining the contact state accompanied by thepivotation by the plurality of flap jigs F. Therefore, it is possible toform an oblique surface portion of a substantially truncated squarebipyramid or a side surface portion of a substantially rectangularparallelepiped using the flap jigs F. In addition, since the flap jigs Fmove to the center side, the container can be formed by folding thefour-sided bag B, and the metal container C can be formed while furtherpreventing the breakage.

In addition, since the two opposing regions of the four regions aresandwiched by the plurality of first flap jigs F1 and the remaining twoopposing regions of the four regions are sandwiched by the plurality ofsecond flap jigs F2, entire surfaces of the containers C1 and C2 havingthe substantially truncated square bipyramidal shape or thesubstantially rectangular parallelepiped shape can be pressed when thecontainers C1 and C2 are formed, the containers C1 and C2 can be formedin the manner of further folding the four-sided bag B, and possibilityof the breakage can be further reduced.

In the process of expanding the volume space inside the four-sided bagB, since the wedge W is operated such that the angle θ formed by theline segment portion W1 and the edge side E changes from the acute angleto the right angle, in forming the containers C1 and C2 having thesubstantially truncated square bipyramidal shape or the substantiallyrectangular parallelepiped shape, the line segment portion W1 of thewedge W can be brought into contact with a portion to be valley-folded,the metal container C can be formed in the manner of further folding thefour-sided bag B, and the possibility of the breakage can be greatlyreduced.

Since the force is applied to the first and second parallel plate jigs11 and 12 and the plurality of flap jigs F in the direction in which theexpansion of the volume space due to the pressurization of the inside ofthe four-sided bag B is prevented, the metal container C can be formedinto a shape corresponding to the first and second parallel plate jigs11 and 12 and the plurality of flap jigs F, and can be formed into thetruncated square bipyramid or the rectangular parallelepiped having aneater shape.

Further, according to the metal container C of the present embodiment,the metal container C in which the breakage due to the local elongationof the metal plate MP is prevented can be made based on the four-sidedbag B.

Although various embodiments have been described above with reference tothe drawings, it is needless to say that the present invention is notlimited to these examples. It will be apparent to those skilled in theart that various changes and modifications may be conceived within thescope of the claims. It is also understood that the various changes andmodifications belong to the technical scope of the present invention.Components in the embodiments described above may be combined freelywithin a range not departing from the spirit of the invention.

For example, in the above-described embodiment, the apparatus 1 formanufacturing the metal container C includes the flap jigs F. However,the present invention is not particularly limited thereto, and themanufacturing apparatus 1 may not include the flap jigs F. In theexample shown in FIGS. 8A to 8D, a step of sandwiching the four-sidedbag B by the first and second parallel plate jigs 11 and 12 and a stepof sandwiching the four-sided bag B by the flap jigs F are performed atthe same time, but the present invention is not limited thereto, and thestep of sandwiching the four-sided bag B by the first and secondparallel plate jigs 11 and 12 may be performed first, or the step ofsandwiching the four-sided bag B by the flap jigs F may be performedfirst.

The four-sided bag B may be formed by a process other than the processshown in FIGS. 7A to 7C, such as superimposing two metal plates MPhaving the same area and welding peripheral edge portions thereof.

Furthermore, since the ear portion D is formed when the container C isformed in the present embodiment, in order to facilitate the formationof the ear portion D, it is preferable that rigidity of (at least a partof) the two opposing sides of the four-sided bag B is lower thanrigidity of the remaining two sides. For example, in the four-sided bagB shown in FIG. 2 , bending rigidity in the plane is high on the longside LS side where the seam welding portion SW is formed, and bendingrigidity in the plane is low on the short side SS side having the edgeside E. Accordingly, when the container C is manufactured from thefour-sided bag B shown in FIG. 2 , the ear portion D is easily formed.

On the other hand, for example, in a case where the container C ismanufactured from the four-sided bag B in which the seam weldingportions SW are formed on four sides, it is preferable that a process ofreducing the bending rigidity in the plane is performed on one of thetwo opposing sides, and the bending rigidity in the plane of (at least apart of) the two sides is set to be lower than in the remaining twosides. FIGS. 9A and 9B are perspective views showing other examples ofthe four-sided bag B, in which FIG. 9A shows a first example, and FIG.9B shows a second example.

As shown in FIG. 9A, for example, rectangular metal plates MP having thesame area are superimposed with each other, and seam welding isperformed on four sides to form the seam welding portions SW, therebymanufacturing the four-sided bag B. When the container C is manufacturedfrom such a four-sided bag B, for example, cut portions N for reducingwidth of the seam welding portions SW are formed on both end sides ofthe seam welding portions SW on two opposing sides (short side SSsides). Accordingly, bending rigidity in the plane at positions (atleast a part of the positions) of the cut portions N can be reduced, andfolding can be easily performed at the positions, so that the earportions D can be easily formed. The cut portion N is formed at aposition away from an end portion VM of the seam welding portion SW by adistance corresponding to half a height of the container C to be finallymanufactured, or at a position closer to the end portion VM than theposition.

Further, as shown in FIG. 9B, for example, the seam welding portions SWon two opposing sides (short side SS sides) may be bent so as to rise orfall. Accordingly, bent portions BE act like the edge side E shown inFIG. 2 , so that bending rigidity in the plane of the bent portions BEcan be reduced, and the ear portion D can be easily formed.

Furthermore, in the present embodiment, the second flap jig F2 includesthe wedge W. However, the present invention is not limited thereto, andthe second flap jig F2 may not include the wedge W. When the wedge W isnot provided, an auxiliary plate AP shown in FIG. 10 may be provided.FIG. 10 is a plan view showing the auxiliary plate AP. As shown in FIG.10 , the auxiliary plate AP is superimposed on the four-sided bag B soas to be aligned with a position where the valley-folded portion VF isformed. Specifically, a plurality of oval holes OV are formed in theauxiliary plate AP. The plurality of oval holes OV change such that theangle θ formed with the edge side E increases (that is, from the acuteangle to the right angle) from an end portion side to a center side ofthe auxiliary plate AP. Such an auxiliary plate AP is superimposed in amanner of being aligned with the position where the valley-foldedportion VF is formed, the formation of the valley-folded portion VF canbe assisted even in the manufacturing apparatus 1 including no wedge W.The auxiliary plate AP is reinforced in the vicinity of the edge side Ehaving lower bending rigidity in the plane than the seam welding portionSW, but is not reinforced in a portion of the oval hole OV. Accordingly,in a part (portion of the oval hole OV), the bending rigidity in theplane is set to be lower than that of the two sides including the seamwelding portions SW.

The metal container C is preferably configured as shown in FIG. 11 .FIG. 11 is an enlarged view of a periphery of an ear portion D accordingto a modification. Although the ear portion D may remain protrudinglaterally, it is preferable that the ear portion D is folded along theside wall HP as shown in FIG. 11 . This is because a shape of the metalcontainer C can be approximated to a substantially rectangularparallelepiped shape or a substantially truncated square bipyramidalshape. If possible, it is preferable that the seam welding portion SW isalso folded along the side wall HP when the ear portion D is folded. Theear portion D is folded to a front side along the side wall HP on a sideincluding the edge side E. However, the present invention is not limitedthereto, and the ear portion D may be folded in an opposite direction.

According to an embodiment, when a container is formed from a four-sidedbag, breakage due to local elongation of a metal plate can be prevented.

1. A method for manufacturing a metal container, comprising: a first step of forming a substantially planar four-sided bag using a metal plate; a second step of sandwiching, by first and second parallel plate jigs, one surface and the other surface of the four-sided bag formed in the first step; and a third step of forming, using the four-sided bag, a container having a substantially truncated square bipyramidal shape or a substantially rectangular parallelepiped shape by pressurizing an inside of the four-sided bag while maintaining a contact state by the first and second parallel plate jigs with respect to the four-sided bag sandwiched between the first and second parallel plate jigs in the second step, and expanding a volume space in the four-sided bag while increasing a distance between the first and second parallel plate jigs.
 2. A method for manufacturing a metal container according to claim 1, wherein in the first step, the four-sided bag is formed such that bending rigidity in a plane of at least a part of two opposing sides is lower than bending rigidity in the plane of remaining two sides.
 3. A method for manufacturing a metal container according to claim 1, wherein in the second step, the one surface and the other surface of the four-sided bag are sandwiched by the first and second parallel plate jigs having a quadrangular shape smaller than an area of the four-sided bag formed in the first step in a plan view of the four-sided bag such that the first and second parallel plate jigs are located inside four sides of the four-sided bag and the four sides of the four-sided bag are parallel to respective sides of the first and second parallel plate jigs, the method further comprises a fourth step, which is executed between the first step and the third step, of sandwiching at least two of four regions around each of regions sandwiched by the first and second parallel plate jigs on the one surface and the other surface of the four-sided bag by a plurality of flap jigs configured to move toward a center side of the four-sided bag while pivoting from a state of being substantially parallel to the first and second parallel plate jigs to a predetermined angle with respect to the parallel state, and in the third step, the four-sided bag is formed with an oblique surface of a substantially truncated square bipyramid or a side surface of a substantially rectangular parallelepiped is formed by pressurizing the inside of the four-sided bag while maintaining a contact state by the plurality of flap jigs with respect to the four-sided bag, which is accompanied by pivotation and movement of the plurality of flap jigs.
 4. A method for manufacturing a metal container according to claim 3, wherein in the fourth step, with respect to a plurality of first flap jigs and a plurality of second flap jigs constituting the plurality of flap jigs, two opposing regions of the four regions are sandwiched by the plurality of first flap jigs, and remaining two opposing regions of the four regions are sandwiched by the plurality of second flap jigs.
 5. A method for manufacturing a metal container according to claim 4, wherein the plurality of second flap jigs include wedges including line segment portions extending from respective vertexes of the first and second parallel plate jigs toward respective sides of the four-sided bag on second flap jig sides on corner portion sides of the four-sided bag, and in the third step, the wedges are operated such that angles formed by the line segment portions and the sides on the second flap jig sides change from an acute angle to a right angle in a process of expanding the volume space in the four-sided bag.
 6. A method for manufacturing a metal container according to claim 2, wherein in the third step, a force is applied to the first and second parallel plate jigs and plurality of flap jigs in a direction in which the expansion of the volume space due to the pressurization in the four-sided bag is prevented.
 7. An apparatus for manufacturing a metal container including first and second parallel plate jigs configured to sandwich one surface and the other surface of a substantially planar four-sided bag formed of a metal plate, wherein the first and second parallel plate jigs each have a quadrangular shape smaller than an area of the four-sided bag in a plan view, are capable of sandwiching the four-sided bag such that the first and second parallel plate jigs are located inside four sides of the four-sided bag and the four sides of the four-sided bag are parallel to respective sides of the first and second parallel plate jigs, and maintain a contact state with the one surface and the other surface of the four-sided bag in a process of expanding a volume space in the four-sided bag by pressurizing an inside of the four-sided bag.
 8. A metal container having a substantially truncated square bipyramidal shape or a substantially rectangular parallelepiped shape, comprising: two quadrangular top plates formed as one surface of the container and the other surface opposite to the one surface; a plurality of side walls connecting the two top plates; and a plurality of ear portions having oblique sides approaching each other from opposing vertexes of the two top plates and protruding laterally or folded along the plurality of side walls, wherein valley-folded portions are formed at boundaries between the plurality of ear portions and the plurality of side walls, and one or more valley-folded marks having the vertex as a rotation center are formed between the valley-folded portion and the oblique side. 